Type the name or coordinates of an object of interest into the "search box" at the top of the page and click on "search". If a name is used, the request is sent to the name resolver at NED (and then other services such as SIMBAD if not found), which returns the coordinates and an image size that are used for the search. Some examples might be:
| M101 | Most objects have a default search radius from NED |
| M87 r=1.0d | You can explicitly change the default search radius |
| Antennae | The resolver recognizes
many names |
| 14h03m12.6s +54d20m56.7s | If no radius is given a default of 0.2 degrees is used |
| 14 03 12.6 54 20 56.7 | Units are optional; equinox must be J2000 |
| 14:03.210 54:20.945 | Many formats are accepted |
| 180.468 -18.866 r=0.4 | Default units are degrees in this case |
| Virgo Cluster | The object can be quite extended |
| 0 0 r=180d | This example is
related to an all-sky
radius problem |
There is also an "advanced search" button to the right that
reveals more options for defining types of data to be returned (e.g.,
instruments; Data Products [e.g. best available, single exposure,
combined, color images]). Note that "best available" selects the data
product that is generally the most useful (e.g., the combined image, if
it exists, rather than the single exposure or color image). There is
also an Image Preference
button.
The following table illustrates the type of available data that is in the HLA. Some are enhanced data products developed for the HLA while others are standard products available from the HST archives.
| Instrument/Product | Source | HLA Enhanced Products | Standard Products |
Download | Interactive Display? |
|---|---|---|---|---|---|
Notes:
|
|||||
| ACS/combined images | STScI | ~90% | FITS | ✔ | |
| ACS/DAOPHOT source lists | STScI | ~50%, <~2004 | Ascii | ✔ | |
| ACS/SExtractor source lists | STScI | ~10%, Beta product1 | Ascii | ✔ | |
| WFPC2/combined images | CADC | ~Coming soon, Beta product1 | FITS | ✔ | |
| WFPC2/single exposures | STScI | 100% | DADS2 | ||
| NICMOS/GRISM extractions | ST-ECF | ~80%, 1-D & 2-D spectra | FITS | ||
| NICMOS images | STScI | 100% | DADS2 | ||
| STIS images and spectra | STScI | 100% | FITS | ✔ | |
| FOS spectra | STScI | 100% | Tar | ||
| GHRS spectra | STScI | 100% | Tar | ||
The tabs just below the search box provide three basic ways to view the results from the search:
INVENTORY (the default) - Shows the results in a table format. Click on the table heading to sort by that value (e.g., "ExpTime"). Clicking again on the same heading reverses the sort order. If there are more than 50 images found, there are controls to go through the table by pages or to jump to the first or last page.
Brief definitions of the table columns are provided at the bottom of
the page; you can also get tool tips by placing your cursor on the
column heading. By default not all of the (many)
table columns are displayed. See instructions on the bottom right to
add, remove, or reposition columns.
A subset of the inventory can be selected using the empty boxes
under
each column heading (e.g. *HRC* will select only ACS/HRC images). Move
the cursor over the empty box for instructions.
The enhanced data products were generated from the original MAST
data. The ACS and WFPC2 images have been combined using multidrizzle,
aligned north up, and been astrometrically corrected when possible
(i.e. approximately 80% of the cases; See the astrometric accuracy FAQ ). Clicking
on the
"Display" link in each row opens the interactive
display for that
image, while "download" allows you to download the FITS data.
When FITS images are not available in the HLA , the display and download options point to the MAST (Multimision Archive at Space Telescope) previews and data files.
IMAGES
- Shows preview images of the results from the "search box" search (or
cutouts if you have used the "advanced search" option). "Interactive
Display" will open a FITS image if available in the HLA. "Mast
Previews" will
open the MAST preview in other cases. The
image (FITS-Science or FITS-MEF; i.e., including only the science image
, or including the image in Multi Extension Format with the science
image in [1], the data quality array in extension [2], and the error
array in extension [3].) There are two types of source lists available;
DAOPHOT (primarily
for point-like objects) and SExtractor (primarily for extended
targets) and a plot button to show some basic plots, when available.
The "more" option in the bottom right provides a wide range of
addition information including the proposal abstract, a list of what
images went into the combined images, and a large number of working
files which are briefly described here
FOOTPRINTS
-Shows footprints of the results from the "search box" search (i.e.,
the outline of various detectors) on a Digital Sky Survey-
2 (DSS-2) image.
There are two important points to keep in mind when using footprints.
Selectable options for the footprint page include:
A table with various information about each image is provided below the footprint image. You can either click on a table row to see the corresponding footprint, or on a footprint to show the corresponding table row. Selected datasets can also be highlighted in the Inventory and Images, and will remain highlighted in all three views.
NICMOS
GRISM - As its first HLA
project, the ST-ECF is working on the extraction of a uniform set of
NICMOS grism (G141) slitless spectra. A sample release of about 80% of
the available fields are available as part of Data Release 1 via the
NICMOS Grism Button or the
interactive display.
INTERACTIVE
DISPLAY - You can look at an image or 2-dimensional spectrum more
carefully, and
overlay a source list, by using the "interactive display" (via either
the inventory or images
view). The image can be
moved by either using the arrows in the upper left (<
>
^ v)
or by dragging the image using the mouse. The o
button recenters. The +
and - buttons zoom in or
out. The Brighter and Darker
buttons change the
contrast. The "invert" button changes from white on black to black on
white. SExtractor or DAOPHOT source lists from the image can be
overlaid by clicking the appropriate
box. A readout showing either the x-y position of the cursor, or
wavelength at the "center" of the image for spectra is in the upper
left. A line or column plot can be made at the location of the cursor
by typing "L" or "C" especially useful for spectra. See the Help in the upper right of
the interactive display for more details.
SOURCE LISTS
-
Two types of source lists are available via the HLA: DAOPHOT, which
is
optimized
for point-like objects, and SExtractor, which is optimized for extended
objects. In both cases the detection image is a "white light image"
(i.e., a combination of images using all available filters within a
single visit, also refered to as the "detection" image). The source
lists can be overlaid on an image using the
interactive display, and can be downloaded via the images
view. The magnitudes are in the ABMAG system. The detection
threshold is roughly 5 sigma. Click here for the
DAOPHOT source list document.
-How to speed up the interactive display
The interactive display can become slow to refresh when moving
around or zooming in or out when a source list is overlaid. Before
zooming or moving, click
the DAOPHOT or SExtractor
box to remove the source list overlay. Once you are where you want to
be, click the box again to add the overlay. This same technique is also
useful for "blinking" the source lists.
In the interest of making the HLA available to proposers at least
one month before the cycle 17 proposal deadline we have scheduled Data
Release 1 for February 8, 2008. There are still a few minor bugs we are
working on, some of which are listed below. We will update this
list if any new items are found after the release.
- Availability of Source Lists
The availability of the source lists on the image page does not always
match what is available in the interactive display. An example is that
source lists may be advertised for the detection images but may not be
present in the interactive display. Conversely, the color image may
indicate that no source list is available to overlay when there
actually is one.
-Radius searching:
The all-sky (0 0r=180) search for all instruments has been temporarily
disabled. This feature will
be restricted to radii of 45 degrees or less for a period following the
initial
release of Data Release 1. It still is possible to perform all-sky
searches for
single instruments.
For each observation, the images have been grouped according to the
filter in which they were obtained, and also according to which camera
was used (eg., obsevations carried out with ACS could be obtained with
either the WFC, HRC or SBC camera).
Each set of images (grouped by filter and camera) is then processed
through the HLA pipeline using the Multidrizzle software (Koekemoer et
al. 2002, HST Calibration Workshop, p.337) which corrects geometric
distortion using the "drizzle" software (Fruchter and Hook 2002, PASP
114, 144), removes cosmic rays and combines the images. For the current
release, the output pixel scale is set to be similar to the input pixel
size (thus 0.05" for ACS/WFC, and 0.025" for ACS/HRC and ACS/SBC).
Smaller pixel scales were precluded primarily on the basis of diskspace
limitations, but are planned for a future release.
Each individual exposure, for all the filters used with a given camera,
is first transformed separately to an undistorted output image, which
are all registered to a common pixel grid (so that objects can be
directly aligned on each image, even if dithering was used).
In addition, all the exposures for a given filter/camera combination
are combined using Multidrizzle into a final, clean image for that
filter/camera combination, which involves identification and removal of
cosmic rays as well as astrometric alignment and distortion removal
using "drizzle".
Finally, if more than one filter was used with a given camera during
the observation, then the exposures from all these filters are combined
into a single "total" image, as long as two or more exposures were
obtained in each filter so that the cosmic ray masks obtained
separately from each filter can be used. These "total" images can
potentially be significantly deeper than the images obtained in each
filter separately, and can be used as detection images with higher
signal-to-noise than the individual filter images in most cases,
although in some cases the combined image for each filter could also be
used as a detection image. Images obtained with grisms or polarizer
filters are excluded from the total image, although they are combined
for each such spectral element separately.
- A paper entitled "The Hubble Legacy Archive: General Description and Validation of Products" will be available. (~February 2008)
- Mosaics: Combined images using data from different visits to produce the deepest possible wide-field images
- A shopping cart so you can select and download several images at the same time
- An advanced search capability to allow you to select classes of objects (e.g., starbursts, irregulars, cepheids, ...)
- An All-HST-Sky Source List
-To be updated March, 2008
All refereed publications based on data obtained from the HLA must carry the following footnote:
Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).
One copy of each paper resulting from data obtained from the HLA should be sent to the STScI.
In addition, publications of research supported by an ST ScI grant must carry the following acknowledgment:
Support for Program number ____________ was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASAcontract NAS5-26555.